When boring out a broken spark plug, what size bit should be used when tapping for the next size bigger plug?

Question

I have a spark plug that broke off in the manifold. Only the threads remain. I plan to drill out the old plug and re-tap the head for a larger plug. what size bit and tap should I use on a 87 kawasaki 600r? Remember this is a metric.

Answer 1

STOP. Before you go to reboring or helicoil, try to remove the fragment of the old plug with a broken scew extractor, (looks like a conical coarse thread screw with a reverse thread). The fragment is already hollow. All you have to do is insert the extractor. Tap it a few times to 'start` it. The apply a wrench and you should be able to screw that 'lil bugger` right on out.
Also note: spark plug thread sizes are pretty close together. The right size drill for the new threads might not remove all the old threads leaving you with a botched head. If you have to drill, helicoil is the way to go. They'll tell you the proper drill size on the package.

Answer 2

what ever you do keep the heli coil out of that thing!!! find yourself a good marine shop and ask for a keen cert set in the size you need.. outboard motors love spitting out spark plugs taking the threads with them,so they ll know what your talking about.but if you can get the broken plug out without screwin up the threads would be your best bet.i just wanna know how you broke a plug off? also remember to vacuum out as much of the aluminum as possable if your unlucky at getting that plug out in one piece,cause i just get the feeling you aint gonna pull that head off(recommended) good luck

Answer 3

There are only two spark plug sizes.

Get a Heli-Coil kit for the same size you use.

http://www.hrpworld.com/index.cfm?form_prod_id=458,76_4351&action=product

Answer 4

use helli coil and use same siz plug...the kit you buy will give size of bit u willl need...good luk